/*
 * Copyright (c) Kumo Inc. and affiliates.
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//
// Docs: https://fburl.com/fbcref_file
//

#pragma once

#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <string>
#include <system_error>

#include <melon/exception_wrapper.h>
#include <melon/expected.h>
#include <melon/portability.h>
#include <melon/range.h>
#include <melon/portability/fcntl.h>
#include <melon/portability/unistd.h>

namespace melon {
    /**
     * A File represents an open file.
     * @class melon::File
     * @refcode melon/docs/examples/melon/File.cpp
     */
    class File {
    public:
        /**
         * Creates an empty File object, for late initialization.
         */
        constexpr File() noexcept : fd_(-1), ownsFd_(false) {
        }

        /**
         * Create a File object from an existing file descriptor.
         *
         * @param fd Existing file descriptor
         * @param ownsFd Takes ownership of the file descriptor if ownsFd is true.
         */
        explicit File(int fd, bool ownsFd = false) noexcept;

        /**
         * Open and create a file object.  Throws on error.
         * Owns the file descriptor implicitly.
         */
        explicit File(const char *name, int flags = O_RDONLY, mode_t mode = 0666);

        explicit File(
            const std::string &name, int flags = O_RDONLY, mode_t mode = 0666);

        explicit File(StringPiece name, int flags = O_RDONLY, mode_t mode = 0666);

        /**
         * All the constructors that are not noexcept can throw std::system_error.
         * This is a helper method to use melon::Expected to chain a file open event
         * to something else you want to do with the open fd.
         */
        template<typename... Args>
        static Expected<File, exception_wrapper> makeFile(Args &&... args) noexcept {
            try {
                return File(std::forward<Args>(args)...);
            } catch (const std::system_error &) {
                return makeUnexpected(exception_wrapper(current_exception()));
            }
        }

        ~File();

        /**
         * Create and return a temporary, owned file (uses tmpfile()).
         */
        static File temporary();

        /**
         * Return the file descriptor, or -1 if the file was closed.
         */
        int fd() const { return fd_; }

        /**
         * Returns 'true' iff the file was successfully opened.
         */
        explicit operator bool() const { return fd_ != -1; }

        /**
         * Duplicate file descriptor and return File that owns it.
         *
         * Duplicated file descriptor does not have close-on-exec flag set,
         * so it is leaked to child processes. Consider using "dupCloseOnExec".
         */
        File dup() const;

        /**
         * Duplicate file descriptor and return File that owns it.
         *
         * This functions creates a descriptor with close-on-exec flag set
         * (where supported, otherwise it is equivalent to "dup").
         */
        File dupCloseOnExec() const;

        /**
         * If we own the file descriptor, close the file and throw on error.
         * Otherwise, do nothing.
         */
        void close();

        /**
         * Closes the file (if owned).  Returns true on success, false (and sets
         * errno) on error.
         */
        bool closeNoThrow();

        /**
         * Returns and releases the file descriptor; no longer owned by this File.
         * Returns -1 if the File object didn't wrap a file.
         */
        int release() noexcept;

        /**
         * Swap this File with another.
         */
        void swap(File &other) noexcept;

        // movable
        File(File &&) noexcept;

        File &operator=(File &&);

        /**
         * FLOCK (INTERPROCESS) LOCKS
         *
         * NOTE THAT THESE LOCKS ARE flock() LOCKS.  That is, they may only be used
         * for inter-process synchronization -- an attempt to acquire a second lock
         * on the same file descriptor from the same process may succeed.  Attempting
         * to acquire a second lock on a different file descriptor for the same file
         * should fail, but some systems might implement flock() using fcntl() locks,
         * in which case it will succeed.
         */
        void lock();

        bool try_lock();

        void unlock();

        void lock_shared();

        bool try_lock_shared();

        void unlock_shared();

    private:
        void doLock(int op);

        bool doTryLock(int op);

        // unique
        File(const File &) = delete;

        File &operator=(const File &) = delete;

        int fd_;
        bool ownsFd_;
    };

    /**
     * Swaps the file descriptors and ownership
     */
    void swap(File &a, File &b) noexcept;
} // namespace melon
